Combination locks are used to secure lockable, high-security enclosures, such as vaults, safes, and cabinets, that afford controlled access to stored items. Mechanical combination locks rely on the rotation of an external dial to manipulate various mechanical elements housed inside a lock casing to register gates in rotatable tumbler wheels or gate wheels with at least one fence carried by a movable fence bar. When the tumbler wheel gates and fences are registered by the entry of a proper combination, the dial may be used to retract a lock bar or dead bolt so that the enclosure can be opened and accessed.
Mechanical combination locks are susceptible to illicit or surreptitious attack by operation of an automatic dialer. The automatic dialer, which is coupled with the lock's dial, systematically dials different combinations of the mechanical combination lock. If a particular combination fails, the automatic dialer proceeds to dial other successive combinations in an attempt to unlock the lock. For example, for a three-tumbler combination lock, the automatic dialer parks one gate wheel at a specific combination number, dials all possible pairs of combination numbers for the other two gate wheels and attempts to retract the dead bolt at each dialed pair, increments the combination number of the first gate wheel, and repeats this process until the proper combination is discovered. Given sufficient time to perform the trial-and-error manipulation, the automatic dialer is particularly effective in compromising the access control afforded by a mechanical combination lock.
Conventional combination scrambler mechanisms have been developed for use in mechanical combination locks that rotate one of the gate wheels as an automatic dialer attempts to systematically dial all possible combinations and to retract the lock bolt at each dialed combination. The rotation of the gate wheel prevents the automatic dialer from parking the gate wheel at a fixed angular location and relying upon that angular location as a reference point. However, conventional combination scrambler mechanisms increment the angular orientation of the gate wheel by an equal angular increment each time that an attempt is made to retract the lock bolt. Because the angular increment is constant and predictable, sophisticated automatic dialers can compensate for changes in the parked angular position of the gate wheel imparted by the combination scrambler by a simple correction factor consisting of the number of attempts multiplied by the constant angular increment.
Mechanical combination locks are also susceptible to surreptitious attack by radiographic imaging methods. Penetrating radiation, such as x-rays and neutrons, can be used to image the internal elements, such as the tumbler wheels and tumbler wheel gates, inside the lock case otherwise hidden from view. As a result, the angular locations of the internal elements, such as the gates, of conventional mechanical combination locks may be observed by radiographic imaging.
The tumbler wheels of mechanical combination locks may be designed to resist radiological detection by, for example, disguising one true gate among multiple false gates each having a similar construction to the true gate. However, conventional false gates are incapable of providing adequate protection or add significantly to the cost of manufacture. In addition, other internal elements, such as fixed-position features on a tumbler wheel or a combination change mechanism, of the mechanical combination lock have a fixed angular position relative to one or more of the gates. The internal elements may be used as fixed reference points or features for determining the angular location of the true gate despite the presence of multiple false gates. As a result, the presence of false gates alone frequently cannot defeat the use of radiographic imaging for determining the angular locations of lock internal elements, such as tumbler wheel gates.
Accordingly, there is a need for combination locks having an increased level of security, while at the same time overcoming many of the shortcomings of conventional mechanical combination locks.